So-called phase-change type optical recording media which achieve optical recording by utilizing a phase-change between a crystalline phase and an amorphous phase are known as one type of rewritable optical recording media. According to this recording system, a recording layer comprising GeTe, In-Se-Tl-Co, Ge-Sb-Te, etc. as proposed to date is irradiated with a light beam, e.g., a semi-conductor laser beam, to be melted and then quenched to form an amorphous phase, which is usually used as a recorded state. The recorded information can be erased by irradiation of a light beam of lower power than used for recording and keeping the recording material at a crystallization temperature for a prescribed time, thereby returning to its crystalline phase.
It is preferred that a recording material to be used in the phase-change type optical recording media should have a short crystallization time for simplifying the optical system and for improving the irradiation speed and also have high stability in its amorphous phase, that is, a high crystallization temperature for retaining the recorded information for a long time.
Of known recording materials applicable to the phase-change type optical recording media, Ge-Sb-Te satisfying the above requirements has been considered one of the best. That is, Ge-Sb-Te disclosed in JP-A-63-225934 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") is a ternary compound synthesized by mixing Sb.sub.2 Te.sub.3 which has a short crystallization time but insufficient amorphous phase stability and GeTe which has high amorphous phase stability but a long crystallization time and is deemed to possess properties intermediate between Sb.sub.2 Te.sub.3 and GeTe.
Nevertheless, Ge-Sb-Te is, though exhibiting some improvements over Sb.sub.2 Te.sub.3, unsatisfactory in amorphous phase stability, still needing an improvement in retention of recorded information.
Besides, a recording material consisting of In, Ge, Sb and Te is disclosed in JP-A-64-14083, which material is prepared by adding In to a composition of Ge-Sb-Te in the form of a single element. However, this recording material has a long crystallization time since the composition of Ge-Sb-Te has a relatively long crystallization time and further the addition of In in the form of a single element renders the resulting NaCl type crystalline structure unstable.